Nugget

In resistance welding, the welding of overlapping pieces of metal at small points by application of pressure and electric current creates a pool of molten metal that quickly cools and solidifies into a round joint known as a nugget. For more information, see resistance spot welding.

Similarly in laser welding, the laser light is absorbed by the material causing a “keyhole effect” as the focused beam drills into, vaporizes, and melts some of the metal. As the pulse ends, the liquefied metal around the keyhole flows back in, solidifying and creating a small spot weld or nugget. The entire process takes just a few milliseconds.  For more information, see laser spot welding.